This invention relates to an internal combustion engine having an overhead camshaft to parts of which lubrication is applied by spraying.
Lubrication of the interface between each cam of an overhead camshaft and the component against which the cam operates e.g. valve stem, tappet, rocker, ultimately controlling the aspiration valves of an internal combustion engine, is often effected by spraying.
The primary objective of such lubrication is to direct a spray of oil on to an intended area of the cam and/or the component against which the cam directly operates. Effective lubrication of the said interface is mainly dependent on maintaining a sufficient oil spray onto the intended area.
The spray is usually emitted from a small hole or jet in a conduit situated conveniently near the said area and fed from the engine oil pump by pipes and/or oilways in the cylinder block and head.
An average engine oil filter is effective in preventing the flow, in the general oil circuits, of particles which would be injurious to sleeve and rolling bearings.
However, it does allow passage of minute particles which in time, become coagulated on the walls of pipes or oilways to form areas of "crust".
Any pieces of this "crust" subsequently dislodged are able to circulate the oilways or pipes and may reach lubrication areas without being influenced by the filter.
While such pieces are usually too soft by their nature to injure sleeve or rolling bearings, they have enough size and tenacity to block the spray holes of the spray lubrication system, thereby starving the cams of their lubrication.
The said pieces may become dislodged purely by the flow of oil in the pipes or oilways, but their incidence is enhanced by the addition of or change to a higher detergent oil than normally used. This is particularly noticeable after the engine has been "flushed out".